This invention relates to the art of abnormal tire condition warning systems and particularly to battery powered systems.
Both over and under inflated conditions in pneumatic tires are a cause for excessive tire wear resulting in premature tire failure. Moreover, such under and over inflated tire conditions can have an adverse affect on the efficiency of operations of the vehicle as to both performance or handling as well as vehicle fuel mileage. Since such conditions and results have been well known for quite some time, there have been many attempts to develop and provide means for automatically detecting and reporting them. Recently, development efforts for a practical and inexpensive device have become more concentrated due to the rise in fuel and tire costs as well as vehicle operation costs in general. Safety continues also to be an important consideration.
While there have been quite a number of prior devices developed and utilized for detecting tire inflation conditions, these prior devices have had structural or operational shortcomings rendering them undesirable or impractical for widespread use. While the specific prior devices may have been many and varied, many have required special wiring and the like extending from the wheel assemblies to the vehicle chassis and then through the vehicle body to the instrument panel. Such wiring adds undesired cost to the system and moreover, is extremely difficult and time consuming to install. Such installation time is particularly important when considered on the basis of installing the devices during original vehicle assembly for making them a part of the original vehicle equipment. Further, the necessary special wiring and associated equipment extending between the wheels and chassis are such that they are susceptible to damage or breakage from road materials, weathering, and the like encountered during normal vehicle use.
There have also been some prior art attempts at developing a detector apparatus self-contained in the wheel assembly to eliminate the necessity for wiring and the like such as the piezoelectric reed transducer power supply system as disclosed, for example, in U.S. Pat. Nos. 4,384,482 and 4,510,484. These devices, associated with a radio transmitter in the wheel assembly and a radio receiver for supplying information to the driver have proven to be effective, but still exhibit characteristics inherent to the piezoelectric reed generators such as slow energy start-up activation, relatively large unit size requirements, expensive costs, and potential variations between individual units. Each of these characteristics can lead to certain operational problems and provide for added costs for the overall system.
Still other systems have attempted to use a battery mounted in-wheel for supplying power to the transmitter. These systems, however, have suffered problems including the size of the battery and the associated operational life of the battery. A battery that could supply the needed energy was impractical due to its size and weight, and a battery with practical physical specifications lacked the energy storage capacity required to provide an adequate continuous service duration and other features often demanded of such a system. With the system being mounted in-tire, frequent battery replacement is very expensive when considering tire dismounting/mounting, wheel balancing, and the cost of the replacement batteries themselves.